The present invention relates to power sharing or xe2x80x9cpower stealingxe2x80x9d for lower voltage control means concurrent with powering a local substantially higher voltage switch.
The prior art has demonstrated certain solutions to the problem of providing lower voltage and current thermostat control means on the same circuit as a substantially higher voltage and current switch which in turn activates HVAC equipment by direct line connection or by relay.
Means for relay line voltage (typically at about 24 vac) powering of the control means are described in U.S. Pat. Nos. 4,078,720 and 5,903,139. U.S. Pat. No. 4,078,720 describes a time variable set point thermostat adapted for use in a two-wire circuit of a heating or cooling system. Electric timer means are connected with a thermostat switch and starting relay means of a transformer having a primary and secondary winding periodically changing the set point of the thermostatic switch at selected intervals. The circuit is arranged to limit the current in the two-wire control circuit to a value less than that required to actuate the starting relay of the heating or cooling system in the two-wire control circuit with the thermostat switch open and to actuate the starting relay when the thermostat switch is closed when the ambient temperature to be regulated varies a determined amount from a selected temperature set point and the thermostatic switch is closed.
U.S. Pat. No. 5,903,139 describes a more sophisticated method of providing a zero point zone xe2x80x9cstealingxe2x80x9d of power so that enough power is taken for storage in high and low voltage capacitors while at the same time maintaining residual power passing to the relay to have continuous operation of heating equipment. A pair of power FETs are connected to the series power terminals, and the gates are controlled by logic and phase timers. FETs are turned off at the end of a phase, while a small amount of power sufficient to operate the control and circuitry is diverted to a power storage circuit, then the FETs are turned back without substantial interruption to the load. One embodiment uses a bi-directional charge pump to transfer power between low- and high-voltage power storage circuits. The circuit can operate with symmetrical or nonsymetrical AC or DC loads. It is significant for the concept of this patent that relatively precise timing of the zone about the zero point be predicted so that the xe2x80x9cstealingxe2x80x9d take place in the very low voltage zones of the continuous voltage curve so as not to cause the relay to be underpowered. The several circuit pieces required to achieve the described result in the patent are subject to failure or off specification operation, thereby increasing the likelihood that the patent device will fail or have a degraded performance. For instance, there are two sets of latches and phase timers critical to operation of the device, in addition to the two back to back FET""s whose cooperative operation is critical to the switching function.
A line voltage solution is described in U.S. Pat. Nos. 4,776,514 and 5,635,896. U.S. Pat. No. 4,776,514 describes a two wire line voltage thermostat with first and second terminals for receiving line voltage power and for connection to a load, a transformer having a current primary winding, a voltage primary winding and a secondary winding, a primary controller connecting the current and voltage primary windings to the terminals, the controller having at least first and second states, the controller in the first state energizing both the current and voltage primary windings and in the second state energizing only the current primary winding, and a temperature responsive circuit connected to the secondary winding for controlling the controller between the first and second states in accordance with sensed temperature such that the load can be energized when the controller is in one of the states and can be deenergized when the controller is in the other of the states. Other prior art describe the unfavorable effect of having transformers associated with the thermostat in terms of increased heat generation, size and cost.
U.S. Pat. No. 5,635,896 describes a communication system with a remote switching module having two signal terminals connected by just two conductors to the signal terminals of a local decoding module. Power is directly provided only to the local decoding module, which applies DC voltage of a first level across the conductors. The remote switching module has a voltage regulator which provides power of a second voltage level lower than the first level for operating a control unit in the switching module. The control unit controls a variable impedance having higher and lower impedance levels and which is connected across the switching module""s signal terminals. The decoding module can detect the different impedance levels by sensing the current flow on the conductors. The switching module communicates with the decoding module by modulating the time intervals between changes in impedance levels. It is clearly disadvantageous to require of two separated modules which results increased installation, manufacture and troubleshooting costs.
The present invention comprises means and methods for power sharing for a lower voltage programmable means for operating a switch which operates at a substantially higher voltage. The present invention is preferably applied to two power line thermostat control of HVAC equipment. Although a programmable thermostat is described in the specific description of the invention as the programmable means, it is intended that the present invention be applicable to other such devices where power is stored by capacitance or in rechargeable batteries for use by lower voltage programmable means while at the same time permitting sufficient current flow through a substantially higher power switch to operate directly or indirectly electrical power equipment. The present invention may be used in the presence of more than two power lines to accomplish HVAC equipment operating, the additional lines being used for other functions.
The present invention is a dramatic simplification of the overly populated circuit of U.S. Pat. No. 5,903,139. The present invention connects the two power lines described above (connected to a low voltage relay or to line voltage) to a bridge rectifier, the output connections of which are connected to a common through the drain and source of an FET. The gate of the FET is activated by a signal from the programmable means, which then causes the current to flow (switches on) through the two power lines to power the relay or directly power the HVAC equipment. The drain of the FET is also connected with power storage means, voltage regulation means and the programmable means. The additional connected means function so that, when the HVAC equipment is operating by FET gate activation, the FET for a very short interval operates to stop current through the source and drain, thereby stopping current flow for a very short interval to the HVAC equipment, thereby delivering DC voltage and current to the power storage means, voltage regulation means and the programmable means. The programmable means preferably operate on power from the power storage means, so that when the HVAC equipment is operating the power storage means are being depleted of power by the programmable means, requiring recharging of the power storage means by shutting off the power to the HVAC equipment for a very short interval so that the power storage means are recharged at least in part.
It is preferable to provide sensing means so that the programmable means may determine an appropriate portion of the alternating current curve from which to take its very short interval of power sharing. The present invention preferably obtains a short and timed portion of DC power from the AC power line inputs substantially after the AC voltage curve rises above or below zero but substantially before the maximum positive or negative voltage is reached.
It is also preferable that when the HVAC equipment is shut off, i.e., the programmable means deactivates the FET so that no current flows to the HVAC equipment directly or indirectly, the power from the two power lines is directly usable by the programming means through a voltage regulation means.